1. Field of the Invention
The present invention relates to a method of and an apparatus for processing graphic data to modify a base separation figure such as a white separation figure, which is often used as a background image area in a prepress process.
2. Description of the Related Art
Soft wrapping materials such as vinyl or cellophane sheets are used for packages, on which color figures and characters are printed. In ordinary printing process using a white printing paper, the density of each halftone image for each color ink is adjusted to reproduce desired colors on a white paper sheet. In the case of the printing on a soft wrapping material, especially on a transparent material, a desired color is not reproduced according to the same method as the printing on a white paper sheet. In order to reproduce a desired color on a soft wrapping material, specific areas corresponding to the color figures and characters to be printed are first painted with white ink, and color inks are then applied on the white-painted areas. These areas to be painted with white ink are referred to as white separation figures.
There are three different types of white separation figures as shown in FIGS. 20(A) through 20(C): a contracted white separation figure shown in FIG. 20(A), an expanded white separation figure shown in FIG. 20(B), and a clipped white separation figure shown in FIG. 20(C). Graphics and characters which are to be printed on the white separation figures are hereinafter referred to as original figures in the specification.
A contracted white separation figure is generated by thinning an original figure by a predetermined width. An outline of the contracted white separation figure, which is actually hidden under the original figure is illustrated by broken lines in FIG. 20(A). The contracted white separation figure effectively prevents white lines from being observed around the original figure when a soft wrapping material expands or shrinks to cause misalignment of printing plates.
An expanded white separation figure is generated by spreading an original figure by a predetermined width (see FIG. 20(B)). Expanded white separation figures are generally created according to various design requirements in printing.
A clipped white separation figure is created when two original figures are in contact with each other (see FIG. 20(C)). The clipped white separation figure is generated by spreading one of the two original figures (a figure representing a letter `H` in the example of FIG. 20(C)) by a predetermined width and cutting the other original figure along a new outline of the clipped white separation figure. This results in a clipped white separation figure formed between the two original figures. In some cases, white images are reproduced by leaving part of the white separation figures without color ink thereon.
FIG. 21 is a plan view illustrating two original figures OFa and OFb and two white separation figures WFa and WFb generated from the original figures OFa and OFb. Both of the white separation figures WFa and WFb are generated according to the above thinning process. When a plurality of original figures are in intimate contact with each other as in the example of FIG. 21, an observable gap is undesirably made between the white separation figures WFa and WFb, and the original figures do not reproduce desirable colors in the gap consequently.
A conventional method manually corrects such white separation figures to bring these white separation figures in direct contact with each other. When original figures and white separation figures have complicated shapes, correction of the white separation figures to appropriate shapes requires the skill and the relatively long time.
Incidentally, basic separation figures other than white separation figures are sometimes used, such as silver separation figures or gold separation figures. The above problem also exists with these basic separation figures.